Cabinet members of the new government are due to be sworn in later on Monday at the National Palace.

Mahathir led a four-party alliance to oust the National Front coalition that has been in power since independence from Britain in 1957 on the back of pledges to fight corruption and institute reforms.

The 92-year-old politician was prime minister for 22 years until 2003 but emerged from retirement to join hands with former political foes amid anger over the 1MDB scandal, involving former Prime minister Najib Razak.

He has reopened a probe into the 1MDB state investment fund.

Mahathir has said initial investigations showed the scale of wrongdoing by Najib's administration was more serious than previously thought.

He said arrests will be made when there is evidence, and there would be "no deal" with Najib.